Magnetic core



March 29, 1949.. J. c. GRANFIELD MAGNETIC CORE Filed March 28, 1946 (OLD ROLLED STEEL COLD IPOZLED Sh'fl Ti 3 ,2 H07 8011.50 5755;

MW :w M Km m ma r n .w 2 t 0 A In N w h H O J u N d 0 7 5 n M Patented Mar. 29, 1949 UNITED STATES PATENT OFFICE 2,465,798 MAGNETIC cons John C. Granfield, Pittsfield, Mass, assignor to General Electric Company, a corporation of New York Application March'28, 1946, Serial No. 657,693

1 Claim. 1

cold rolled hydrogen-annealed silicon steels have been developed which have substantially lower specific losses and higher permeability in the direction of rolling than does the hot rolled steel, especially at the comparatively high flux densities at which the cores of modern induction apparatus are operated. However, a core made of the cold rolled steel is substantially noisier than,

certain proportion of lamination layers of hot rolled steel and the remainder of cold rolled silicon steel would have properties corresponding to the average of similarly dimensioned cores, the same proportion of which are made entirely of hot rolled steel and the remainder of which are made entirely of cold rolled steel. Unexpectedly, however, that is not the case. For example, a core having alternate laminations, or equal numbered groups of laminations, of the different materials has lower exciting current and losses at the same value of flux than the average exciting current and losses of two similar cores, one of which is made entirely of the hot rolled steel, and the other of which is made entirely of the cold rolled steel. This, therefore, is a more effective way to use the cold rolled steel in that the total reduction in losses per pound of the cold rolled steel will be greater when it is mixed in interleaved lamination layers with the hot rolled steel than when it is used alone.

The reason for the above mentioned, unexpected result is believed to be that the higher permeability cold rolled steel operates at higher than average flux density while the hot rolled steel consequently operates at lower than average flux density. As the difference between the losses per unit volume or weight of the two materials increases in favor of the cold rolled steel as their flux density increases, the unequal flux density in the two materials substantially reduces the losses in the hot rolled steel and causes a relatively small increase in the losses in the cold rolled steel.

Furthermore, I have found that a still more effective use of the cold rolled steel can be made by concentrating it in the outer lamination layers of the core instead of distributing it more or less uniformly through the core. This is because the flux density in the outer portion of the leg of a homogeneous laminated core is higher than in the center portion. Consequently, when the high permeability low loss material is in the outer portion of the core, the natural inequality in flux distribution is added to the inequality in flux distribution caused by the different materials. This is confirmed by the fact that when the relative position of the two materials is reversed and the cold rolled steel is concentrated in the center laminations and the hot rolled steel is concentrated in the outer laminations, the losses are higher than and the permeability is lower than if the materials are evenly mixed throughout the core cross section.

When the core is of the stepped or cruciform cross section type in which the center laminations are wider than the outer laminations, the amount of cold rolled steel in the outer laminations or steps is relatively small in comparison with the amount of hot rolled steel in the center part of the core, and I have found that this is a very effective way to use the relatively expensive cold rolled hydrogen-annealed silicon strip steel. Such a core is not much noisier than a core made entirely of hot rolled steel lamination layers.

Another advantage of using the cold rolled steel in the outer core laminations is that it reduces the leakage of flux from the core and its resultant stray losses, especially at the higher values of flux density. This is because the higher permeability material, which tends to retain the flux, is between the lower permeability core material and the surrounding material.

An object of the invention is to provide a new and improved magnetic core.

Another object of the invention is to provide a magnetic core having lamination layers of different magnetic materials.

A further object of the invention is to provide a magnetic core in which hot and cold rolled silicon steel lamination layers are distributed in economical proportions.

An additional object of the invention is to provide an economical magnetic core having relatively low losses.

The invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the drawing, Fig. 1 is a perspective view of a transformer having a core embodying my invention, and Fig. 2 is a sectional view taken on line 2-2 of Fig. 1. Referring now to the drawing, there is shown therein a transformer comprising by way of example a two-legged, magnetic core 1 whose leg portions 2 and 3 are joined by upper and lower yoke portions 4 and 5 and which are surrounded by concentric coils or windings 6 which are shown in perspective on leg 2 and in cross section on leg 3.

In order to obtain good space factor in the coil windows, the core is made of a step or cruciform cross section as is shown most clearly in Fig. 2 in which there is a relatively thick center section 7 of the widest laminations. On opposite sides of this center section are duplicate, slightly narrower and thinner sections 8 of laminations. On the outside of these are in turn duplicate narrower steps or sections 9, l0 and I I The center portion of the core consists of laminations of hot rolled silicon steel and the outer portions of the core consist of laminations of the cold rolled silicon steel. I have found that in a five-stepped construction, such as is illustrated, very good results are obtained if the two outer steps designated by 10 and H in Fig. 2 are made of laminations of cold rolled hydrogen-annealed silicon steel, while the intermediate steps or sections are made of hot rolled silicon steel.

The material in any given lamination layer in the core is the same throughout that layer. The

joints at the corner of each step or section may be made in any well-known manner, such as by a conventional alternate butt and overlap joint or by a miter joint. Furthermore, the core may also be made by nesting together a plurality of different Width, wound cores so as to form a cruciform cross section as shown in Fig. 2. In any case, I have found that the placing of a relatively small amount of high permeability low loss magnetic material in the outer lamination layers of the core and making the rest of the core of relatively low permeability high loss hot rolled silicon steel produces a core having relatively low losses and exciting current and reasonable quietness. The actual watts reduction in transformer core loss per pound of cold rolled steel which is obtained by such use of cold rolled silicon steel is greater than can be obtained by making a given core entirely out of cold rolled silicon steel instead of out of hot rolled silicon steel.

While there have been shown and described particular embodiments of this invention, it Will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the invention and, therefore, it is aimed in the appended claim to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

A magnetic core comprising a plurality of lamination layers forming a closed loop magnetic circuit of cruciform cross section made up of a central step of a plurality of Wide laminations flanked on opposite sides by a plurality of steps of progressively narrower laminations, the widest laminations which make up the central step being made of hot rolled silicon steel, the narrowest laminations which make up the outermost steps being made of cold rolled silicon steel.

JOHN C. GRANFIELD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 852,712 Frank May 7, 1907 1,731,861 McRell Oct. 15, 1929 1,896,762 Whittle Feb. 7, 1933 1,982,344 Kinnard Nov. 27, 1934 

